This invention relates to a method of treating a permeable structure such as a permeable subterranean formation using water-soluble organic copolymers containing N-vinylpyrrolidone in the copolymer repeat units in order to stabilize, in the structure, migrating fines such as silica, iron minerals, and alkaline earth metal carbonates.
The recovery of fluids such as oil or gas or combinations thereof has been troublesome in areas where the subterranean formation is composed of one or more layers or zones which contain migrating fines such as silica, iron materials, and alkaline earth metal carbonates. These fines tend to move or migrate to the well bore during the recovery of formation fluids from the particular layers or zones and frequently the migrating fines block the passageways leading to the well bore. The movement or migration of fines to the well bore is a particular problem when the fines are contacted with water foreign to the formation. Plugging or materially impairing the flow of the formation fluids towards the well bore results in a loss of these fluids to the producer and decreases the rate of hydrocarbon recovery from the well which may cause the well to be shut down because it is economically unattractive to produce therefrom. An additional adverse factor resulting from the movement of the fines towards the well bore is that they are often carried along with the formation fluids to the well bore and pass through pipes, pumps, etc., being used to recover the formation fluids to the surface with resulting damage to the moving parts as the fines are very abrasive.
Secondary and tertiary methods of recovering hydrocarbons from a subterranean formation are well known. In general, such a method involves introducing a fluid, such as water, steam, etc., into one or more injection wells which penetrate the formation and forcing the fluid toward one or more offset producing wells. Migrating fine particles during such an operation can decrease the permeability of the formation which may cause a decrease in the rate in which fluid can be injected into the formation which results in a decrease in the rate of hydrocarbon production at the offset production wells.
Migrating fine particles are frequently encountered during acidizing or fracturing operations and during sand consolidation operations. The presence of migrating fine particles during these operations can result in a decrease in the permeability of the formation which is being treated.
Gravel packing is a widely practiced method of preventing the production of sand from poorly consolidated formations. The migration of fine particles into the gravel pack can greatly reduce the permeability of the gravel pack. This can result in a decrease in the rate of production of hydrocarbons from the formation.
Consequently, in efforts to overcome these problems, various methods have been developed for treating a subterranean formation in order to stabilize portions of the formation containing migrating fines. For instance, U.S. Pat. Nos. 4,366,071; 4,366,072; 4,366,073; 4,366,074; and 4,374,739 disclose the use of organic polycationic polymers to prevent or reduce the ill effects of swelling clays or migrating fines or combinations thereof in subterranean formations. These patents are assigned to the assignee of the present invention and are hereby incorporated by reference.
The present invention provides a method of stabilizing fines within a consolidated structure such as a subterranean formation using organic copolymers which are effective in reducing the migration of fine particles in the consolidated structure. The copolymers can be either nonionic in a neutral media or can contain up to 20 percent by weight of a cationic monomer.